Method of forming a printing plate



2,962,961 METHOD or FORMING A PRINTING PLATE Valentin Diet z, .Boedigheim, Badischer Odenwald, Germany, assignor to Dilith Corporation, Societe Anonyme, Luxembourg, Luxembourg, a corporation of Luxembourg No Drawing. Filed Jan. 28, 1954, e r. No. 406,874; 1 Claim. (Cl.-101-1,49.2)

The present invention relates to a new and improved process for forming a printing platefor intaglio and flat printing. i

It is one object of this invention 'to provide a new and improved surface and intaglio printing process which can be carried out in a simple and lefieetive manner-,and which produces long runs of clear prints with sharply defined contours.

Other o j Qf-th s in en ion a d adv n a ou tures thereof will become apparent as the .dfiSCription proceeds.

According to the process of this invention the carrier or support of the image, design, or lettering to be printed is provided with a tannable or hardenable, image-receptive gelatin layer the thickness of which in the swollen state must not exceed about 0.1 mm. Such an extremely thin colloidal layer is first subjected to preliminary tanning or hardening treatment in such a manner that the image, design, or lettering subsequently applied to said pre-tanned or pre-hardened colloidal layer is also subjected to a certain degree of preliminary tanning or hardening. Said preliminary tanning or hardening treatment renders the colloidal layer extremely stable and durable so that it does no longer dissolve even when exposed to the action of boiling water. Provision of such an extremely thin colloidal layer prevents too deep a final image-fixing tanning or hardening and, consequently, too deep an impression of the image, design, or lettering to be printed and, thus, produces especially sharp prints.

Extensive experiments have shown that exposure to light which, heretofore, was considered as being essential, can be eliminated and replaced by incorporating into the pre-tanned or pre-hardened, very thin colloidal layer compounds which change the image, design, or lettering produced on the colloidal layer, by chemical reaction.

For this purpose, chromic acid or its salts are added to the writing, drawing, or image-forming agent, such as typewriter ribbon, ink or the like. On the other hand, small amounts of a reducing agent capable of reducing chromic acid, such as, for instance, hydroxylamine hydrochloride, monomethyl p-amino phenol sulfate or the like, are added to the pre-tanned or pro-hardened, 'very thin tannable or hardenable colloidal layer. On drawing or writing on said layer, chromic acid present in the drawing, writing, or image-forming agent encounters the reducing agent present in said layer and is reduced, even in the absence of actinic light, at the marked areas, thereby forming chromic chromate or other chromium salts of lower degree of oxidation. The course of said reduction reaction is revealed by a brownish discoloration of the originally yellow image, design, or lettering. Said reduction reaction proceeds, even in the dark, much quicker than the reaction caused by exposing the layer to light. It is advisable to apply the reducing agent only after the image, design, or lettering has been drawn or written on said colloidal carrier and after any required corrections have been made.

To carry out the process according to the present in- Ce Patented Dec. 6, 1960 2 ventiqn, h image. d ign. o l tteri g to be printed is directly drawn for written on the re-tanned .01 prehardened, very .thin colloidal layer .by means of a bichromate containing writing, drawing, or image-formingagent, when said printing surface is used in .olfset printing. Or the imagefdesign, or lettering to be printedlis first drawn or written on a piece of paper by means ofabichromate containing writing, .or drawing, .or other imagerforrning agent and said original is then transferred to the moistcried and slightly driedpre-tanned or pm-hardened, very thin colloidal layer to form thereon an image, designer lettering in reverse, in easesaid colloidal ,printingsurface is used in direct printing. In both .cases, the entire image, design, or lettering is coated with a sol tion, for instanc of -4 g. efhydrazine hyd oc oride,

20 of ydroqu none,

2 g. of sodium hydroxide,

'55 ccpfrvater, and

924 cc. of alcohol.

Said solution, almost instantaneously, causes tanning or hardening of the image, design, or lettering.

Such a final tanning or hardening due to the action of the reducing agent is new and of utmost importance since it renders the printing process independent from a source of light and since it can be carried out with considerably greater speed. This is of great advantage for the layman using this method of reproduction in his office.

Printing surfaces according to the present invention are far superior to other known printing surfaces in that they tenaciously retain the greasy image-fanning ma terial, that they will not tone-up during use, that the images, designs, or lettering produced thereon will not fall oif during use, that they will withstand considerably more pressure without distortion than heretofore produced images, designs, or lettering, that said surfaces will permit erasure without the use of liquids and without showing the erasure, that they have a remarkably long service life, that they will produce prints of extraordinary sharpness and definition, even in long runs, and that they have other greatly improved characteristics.

The term tanning as used herein and in the claims annexed hereto, refers to a treatment of the water soluble colloidal layer whereby its water solubility is reduced and it is hardened.

The preliminary tanning or hardening treatment is preferably effected by means of formaldehyde. Care must be taken not to cause too strong a tanning or hardening of the colloidal layer because, in this case, the colloidal layer will accept the printing ink not only at those places where the image, design, or lettering has been produced 'by subsequent tanning or hardening of said colloidal layer but also at those other places exposed to such excessive preliminary hardening. The colloidal layer must also not be too soft because then it is not suitable for the production of sufficiently long runs due to a disintegration of the colloidal layer on printing.

Subsequent tanning or hardening to fix the image, design, or lettering to the colloidal layer requires a degree of tanning or hardening which prevents the image, design, or lettering from dissolving and disintegrating in the course of the normal printing procedure.

In general, as explained hereinbefore, two ways of producing the image, design, or lettering on the prehardened colloidal layer have proved to yield the desired results:

(a) The pre-tanned or pre-hardened, very thin colloidal layer does not contain a reducing agent. The image-forming agent, for instance, the typewriter ribbon contains potassium bichromate. Writing with said bichromate containing ribbon on the colloidal layer produces thereon the image. Final image-fixing tanning or hardening of the colloidal layer at those places where the image to be printed has been written on is effected when moistening the colloidal layer and the image thereon with a reducing agent, such as hydroxylamine hydrochloride.

(b) According to another embodiment of this invention, as explained above, the pre-hardened colloidal layer is first moistened with a solution of said reducing agent. When writing on such a layer with a typewriter ribbon containing potassium bichromate therein, tanning or hardening of the image sets in instantaneously. Heretofore, such instantaneous production of an image, design, or lettering on a colloidal layer for subsequent printing was not possible. The most preferred agents for producing a printable image, design, or lettering on a prehardened colloidal layer are alkali bichromates and hydroxylamine salts although other agents, as explained hereinbefore, may also be used.

Iclaim:

In a method of forming a printing plate for fiat and intaglio printing, the steps comprising placing a gelatin layer on a supporting backing, partially hardening said layer by treating with a tanning agent, printing on said layer with an image forming agent, containing a compound seleoted from the group consisting of chromic acid and salts thereof, coating said printed layer with an agent capable of reducing said image forming agent, the reducing agent being selected from the group consisting of hydroxyl amine salts and monomethyl p-arninophenol sulfate, whereby the portions of said printed layer contacted by said image forming agent are hardened and caused to shrink.

References Cited in the file of this patent UNITED STATES PATENTS 134,470 Edwards Dec. 31, 1872 1,453,259 John Apr. 24, 1923 1,521,509 Dorel Dec. 30, 1924 1,625,714 DeSperati Apr. 19, 1927 2,044,156 Dietz June 16, 1935 2,291,673 Alberts et a1. Aug. 4, 1942 2,311,809 Bassist Feb. 23, 1943 2,322,136 Jahoda June 15, 1943 2,393,378 Jahoda et a1. Jan. 22, 1946 2,412,889 Jahoda Dec. 17, 1946 FOREIGN PATENTS 249,707 Great Britain Apr. 1, 1929 OTHER REFERENCES Clerc: Ilford Manual of Process Work, 4th ed., 1946, published by Ilford, London, p. 122. 

